OK, I tried the boiling water. Added a half inch to a cup, put in 2
stamps and put it in the microwave & nuked them. Brought it to a boil
then let set until the water was cold again. One with a very light
stain came out quite well, not noticable at all. The other with a much
heavier stain did not come out. Neither appear to my untrained eye to
have been adversley affected by the boiling.
So now I'll give vinegar, hydrogen peroxide and a diluted clorox mix a shot.